Originally Posted by Kilgore
You can just guess at some corrections and then do another full set of grayscale measures, and keep repeating until you get a gamma reading you want.
This may not be necessary. You can display the %stimulus pattern in question, e.g. a 70% window, use free measurement to observe the measured xyY value while changing your gamma setting for 70% in the TV/projector, and align the measured Y to the target gamma Y as shown in the measurement table.
If you suspect the 100% luminance level is changed, you can check the box "Editable data" in the measurement table, do a free measurement at the 100% pattern, copy-and-paste the measured xyY data (on the left side of the screen) to the column of 100% data, and all the target gamma Y values for 10% - 90% will be refreshed.
Of course, this will work only if you have done a complete grayscale run; and the process is too clumbersome.